Generally, pulp substantially devoid of black liquor is obtained by water washing of pulp containing black liquor. Various descriptions of water washing of pulp containing black liquor are found, for example, within U.S. Pat. Nos. 6,074,522, 6,159,338 and 5,753,074. A continuous diffuser for washing pulp is presented within U.S. Pat. No. 5,778,704. These procedures produce pulp substantially devoid of black liquor and recovery of black liquor, diluted by water
Therefore, an object of this invention is to obviate many of the limitations and disadvantages of the prior art.
This invention relates to production of pulp, substantially devoid of black liquor, and recovery of black liquor, undiluted by water.
An important object of this invention is to supply an organic solvent forming a layer within a vessel.
A significant object of this invention is wherein the organic solvent layer remains within the vessel.
A primary object of this invention is creation of pulp, substantially devoid of black liquor.
A secondary object of this invention wherein the organic solvent is a mixture of organic solvents which establish density.
A characteristic object of this invention is wherein the organic solvent performs separation of materials of dissimilar composition having individual densities.
An additional object of this invention is to perform this invention continuously at atmospheric pressure.
Another object of this invention is recovery of black liquor, undiluted by water.
Yet another object of this invention is to essentially separate pulp from black liquor.
With the above and other objects in view, this invention relates to the novel features and alternatives and combinations presently described in the brief description of the invention.
Pulp, containing black liquor, obtained from digestion of wood chips, is composed fundamentally of cellulose. The pulp, must be removed from black liquor to create brown pulp substantially free of black liquor. Separation of pulp from black liquor is achieved by a difference in density of the main components. An organic solvent, of density greater than that of pulp and less than that of aqueous sodium compounds within black liquor is utilized for separation. Purposely the solvent is insoluble in both components. The organic solvent, as a layer, remains in place to separate pulp under the layer and separate black liquor over the layer. The organic solvent is customarily selected from the group consisting of halogen compounds and hydrocarbon compounds including an individual or combination thereof. Density of chlorinated solvents, reported within, xe2x80x9cProduct Stewardship Manual,xe2x80x9d supplied by Dow Chemical Company, appendix B, gives a specific gravity range of chlorinated solvents as 1.32 to 1.62, with a water solubility ranging in percent from 1.70 to 0.015. Black liquor, containing a trace of dissolved chlorinated solvents, may require water washing or distillation to recover and recycle the chlorinated solvents.
Cellulose density, reported within Handbook of Chemistry and Physics, 56th edition 1975-1976, page C-236 is about 1.3-1.6 grams/cc. Pulp consisting ordinarily of cellulose and hemicellulose has a similar density of about 1.3-1.6 grams/cc.
Black liquor, containing aqueous sodium compounds is of somewhat variable density, which is characterized by sodium hydroxide concentration, op cit., page D-256. Sodium hydroxide concentrations varying from 0.10% to 0.20% and densities ranging to 1.1109 to 1.2214 depend on sodium hydroxide concentration similar to that of black liquor.
Pulp, containing black liquor is thus separated from black liquor without filtration with water and subsequent dilution of black liquor. The net result is to obtain brown pulp substantially free of black liquor.
The present invention, in its broadest aspect, is a method to produce pulp substantially free of black liquor is described, which comprises: providing a vessel, and an organic solvent for forming a layer of the organic solvent within the vessel and pulp containing black liquor. Upon adding pulp containing black liquor within the layer will form three layers, and removing pulp substantially free of black liquor from the lower layer, and removing black liquor substantially free of pulp from the upper layer, and retaining the organic solvent in place, whereby pulp containing black liquor is separated to create pulp substantially free of black liquor and provides black liquor from the organic solvent
Key features of this invention are:
Organic solvent forms a layer within a vessel.
The organic solvent is restrained within a vessel.
The organic solvent is of a density greater than that of black liquor, and less than that of pulp.
The organic solvent is often a mixture of organic solvents to establish density.
The organic solvent performs separation of materials of dissimilar composition having individual densities.
Generating pulp, substantially free of black liquor, obtained from an organic solvent.
Creating black liquor, substantially free of pulp, obtained from an organic solvent.
Separating pulp containing black liquor.
Pulp, substantially free of black liquor containing dissolved organic solvent, may require distillation to recycle the organic solvent.
Pulp, substantially free of black liquor, containing dissolved organic solvent, is occasionally washed with water to remove traces of the organic solvent adhering to the pulp.
Black liquor, after separation, maintains its concentration and is undiluted by water washing.
The method is accomplished at atmospheric pressure.
The method is practiced in a continuous fashion.
The vessel utilized is often a settling tank.
Pulp substantially free of black liquor is subjected to bleaching.
Pulp substantially free of black liquor is subjected to a fourdrinier.